1. Field of the Invention
The present invention relates to a rubbing apparatus for a liquid crystal display panel and, more particularly, to a rubbing apparatus for a liquid crystal display panel and method of aging rubbing cloth for rubbing an alignment film formed on a large-scale mother substrate using an automated system.
2. Description of the Related Art
In general, a liquid crystal display is a display device in which data signals having image information are individually supplied to pixels arranged in a matrix form and light transmittance of the pixels is controlled to thereby display a desired image.
Thus, the liquid crystal display includes a liquid crystal display panel on which pixels are arranged in a matrix form and a driving circuit for driving the pixels.
A liquid crystal display panel includes a thin film transistor array substrate and an attached color filter substrate with a uniform cell gap therebetween in a facing manner, and a liquid crystal layer formed in the separated gap between the color filter substrate and the thin film transistor array substrate.
An alignment film is formed at each facing surface of the thin film transistor array substrate and the color filter substrate, and a rubbing process proceeds on the alignment film so that liquid crystals of the liquid crystal layer may be arranged in a certain direction on the alignment film.
A common electrode and a pixel electrode are formed in the liquid crystal display panel as the thin film transistor array substrate and the color filter substrate are attached, in order to apply an electric field to the liquid crystal layer.
If a voltage is applied to the common electrode, when a voltage of a data signal applied to the pixel electrode is controlled, liquid crystals of the liquid crystal layer are rotated by dielectric anisotropy according to the electric field between the common electrode and the pixel electrode, in order to transmit or block light by the pixels to thereby display a text or an image.
A fabrication process of the liquid crystal display panel in accordance with a related art will now be described in detail.
Though not shown, in the fabrication process of the liquid crystal display panel, first, thin film transistor array substrates are formed on a first mother substrate, and color filter substrates are formed on a second mother substrate.
Pixels are arranged in a matrix form on each thin film transistor array substrate. A thin film transistor, a pixel electrode and a capacitor are formed at each unit pixel of each thin film transistor array substrate. A common electrode, a color filter and a black matrix are patterned on each color filter substrate.
After an alignment film is formed at each surface of the first and second mother substrates, a rubbing process is performed. In the rubbing process, a rubbing cloth rubs the surface of the alignment film with uniform pressure at a uniform speed, so that polymer chains at the surface of the alignment film are aligned in a certain direction and liquid crystals are arranged in a certain direction.
Subsequently, the alignment films respectively formed at each surface of the first and second mother substrates are attached in a facing manner to fabricate a plurality of liquid crystal display panels. In this case, a spacer is formed between the first and second mother substrates to have a uniform cell gap therebetween.
Then, the first and second mother substrates, attached as described above, are cut and processed to separate the plurality of liquid crystal display panels.
A method of rubbing the alignment film according to a related art will be described in detail with reference to FIG. 1 as follows.
FIG. 1 is a view showing an example of rubbing the alignment film formed on the large-scale mother substrate in accordance with a related art.
As shown in FIG. 1, in the related art method for rubbing the alignment film, first, after an alignment film 11 formed of polyimide or the like is formed on a mother substrate 10, a roller 14 with rubbing cloth 13 wound thereon is installed to be inclined at a certain angle (θ) from a longer side of the mother substrate 10. Then, the rubbing cloth 13 is rubbed on the alignment film 11 by moving the mother substrate 10 in a direction parallel to the longer side of the mother substrate 10, thereby rubbing the alignment film 11.
In this case, before a new rubbing cloth wound on the roller 14 is used during a mass production of liquid crystal display panels, it is subjected to an alignment process in which it is rubbed on a dummy substrate for a certain time. But if the new rubbing cloth is directly used in the mass production without the rubbing cloth alignment process, defective rubbing may occur in the direction parallel to the longer side of the mother substrate 10 on the alignment film due to non-alignment of the new rubbing cloth.
Moreover, the rubbing cloth alignment process can be also performed when defective rubbing occurs on the alignment film 11 formed on the mother substrate 10 during the actual mass production of the liquid crystal display panels. Namely, if a defective rubbing on the alignment film 11 is detected during a process of the actual mass production where the alignment film 11 formed on the mother substrate 10 is rubbed by applying the rubbing cloth 13 which has already undergone the rubbing cloth alignment process, the process of aligning the rubbing cloth 13 by rubbing it on the dummy substrate for certain time is performed again to remove the rubbing-defective portion of the alignment film 11.
The dummy substrate is made of the substantially same material and has the same size as the mother substrate 10 used for the actual mass production.
FIG. 2 is an exemplary view showing a layout of a rubbing apparatus of a liquid crystal display panel in accordance with the related art.
As shown in FIG. 2, the rubbing apparatus for the liquid crystal display panels includes at least one cassette 21 for keeping mother substrates to be rubbed, a plurality of rubbing units 22 for receiving the mother substrates kept in the cassettes 21 and for performing a rubbing thereon, a robot 23 for conveying or returning the mother substrates kept in the cassettes 21 or mother substrates that have been rubbed by the rubbing units 22, and an external port 24 for keeping dummy substrates to be aligned by the rubbing cloth.
Herein, the dummy substrates kept at the external port 24 are transferred to or returned from the rubbing units 22 by a manual operation of an operator.
The rubbing units 22 receive the mother substrates to be subjected to rubbing from the robot 23 and perform rubbing thereon. In general, the rubbing cloth is replaced with a new one after rubbing 400 sheets of mother substrates.
As mentioned above, the replaced new rubbing cloth needs to undergo the alignment process where it is rubbed on the dummy substrate for a certain time, before performing rubbing on the mother substrates. For the new rubbing cloth to be aligned, the operator manually transfers the dummy substrates kept in the external port 24 to the rubbing unit 22, and after the rubbing cloth alignment process is completed, the operator manually returns the dummy substrates to the external port 24 from the rubbing units 22.
If defective rubbing of the mother substrates is detected after the mother substrates are rubbed in the rubbing unit 22, the operator can manually move the dummy substrates kept in the external port 24 to the rubbing units 22 to perform the alignment process by rubbing the rubbing cloth on the dummy substrates for a certain time again, in order to remove a rubbing-defective portion of the mother substrates.
After the rubbing cloth re-alignment process is completed, the operator manually returns the dummy substrates to the external port 24 from the rubbing units 22.
As mentioned above, the above rubbing apparatus has the following problems.
In order to perform the rubbing cloth alignment process, the operator should manually transfer the dummy substrate kept in the external port to the rubbing unit, and then, after the rubbing cloth alignment is completed, the operator should manually return the dummy substrate from the rubbing unit. This causes the operator an inconvenience, increases fatigue and delays the time required for transferring or returning the dummy substrate, resulting in the degradation of productivity.
As the mother substrates increase in size in line with the trend of large-scale liquid crystal display panels, the size of the dummy substrate increases, making it very difficult for the operator to manually transfer or return the dummy substrate, and in a worst case, it may not be possible to transfer or return the dummy substrate.